Manufacturers of mechanical and hydraulic equipment regularly increase the viscometric requirements for lubricating compositions used in such equipment. These increases are driven by a desire for reduced maintenance and lubricating composition replacement, a desire for and laws and regulations for reduced environmental emissions, and by the closer tolerances of moving parts, higher operating temperatures, and other changes in new equipment designs.
Manufacturing a lubricating composition that meets more stringent viscometric requirements is typically more expensive than manufacturing a lubricating composition meeting less stringent viscometric requirements. This may be due to both a higher priced feed to such a process and additional or more expensive processing involved in such manufacturing. A high viscosity index ("VI") is a key measure of a superior lubricating composition. "High VI" is defined in detail later in this specification. High VI lubricating compositions have traditionally been manufactured synthetically from polymers. The addition of polymeric VI improvers also has been traditionally employed to improve the VI performance of mineral oils. These are expensive ways, however, to obtain a lubricating composition having a high VI.
It would be advantageous to have a relatively inexpensive process for producing high VI lubricating compositions. Such a process would ideally utilize a readily available inexpensive feedstock. Waste plastics/polymers have been used in known processes for the manufacture of some synthetic hydrocarbons, typically fuels or other polymers.
According to the latest report from the Office of Solid Waste, USEPA, about 62% of plastic packaging in the U.S. is made of polyethylene, the preferred feed for a plastics to lubes process. Equally important, plastics waste (after recycling) is the fastest growing waste product with about 18 million tons/yr in 1995 compared to only 4 million tons/yr in 1970. This presents a unique opportunity, not only to acquire a useful source of high quality lube, but also address a growing environmental problem at the same time.
Dewaxing is required when highly paraffinic oils are to be used in products which need to remain mobile at low temperatures, e.g., lubricating oils, heating oils and jet fuels. The higher molecular weight straight chain normal and slightly branched paraffins which are present in oils of this kind are waxes which cause high pour points and high cloud points in the oils. If adequately low pour points are to be obtained, these waxes must be wholly or partly removed.
Methods are known for upgrading to lubricating compositions various waxy feeds by dewaxing. Various solvent removal techniques are known, such as propane dewaxing and MEK dewaxing but these techniques are costly and time consuming. Solvent dewaxing removes waxes by dissolving them in the solvent, then separating the solvent containing the dissolved wax from the lube oil range material. Where a major portion of the feed is wax, solvent dewaxing leaves only the minor portion of lube oil remaining.
Catalytic dewaxing, on the other hand, does not separate out waxes, but rather converts them to light products boiling below the lube oil range. The conversion is achieved by selectively cracking the longer chain waxy molecules to produce lower molecular weight products, some of which may be removed by distillation. Isomerization catalytic dewaxing is another form of catalytic dewaxing. It is superior to other dewaxing methods. Isomerization catalytic dewaxing achieves a lower pour point neither by removing the wax nor by cracking the wax. Rather, it achieves a lower pour point by isomerizing the wax. Isomerization dewaxing is taught in U.S. Pat. No. 5,135,638 (the '638 patent). However, the '638 patent does not teach the use of isomerization dewaxing for a feed derived from a waste plastics feed.
EP patent application 0620264A2 discloses a process for making a lube oil from waste plastics. The process utilizes a cracking process in a fluidized bed of inert solids and fluidized with, e.g., nitrogen. The product of the cracking is hydrotreated over an alumina catalyst or other refractory metal oxide support containing a metal component, and then optionally catalytically isomerized. The overall yield, however, is lower than desired. The isomerization catalysts taught partially cause this result. There is no teaching of using better isomerization catalysts. Also, EP 0620264A2 does not teach a process of producing a high yield of heavy lube oils.
It would be advantageous to have a process using readily available waste plastics to produce a high yield of high VI lubricating oil compositions, especially heavy high VI lubricating oil compositions. The process of the present invention meets this need.